Why Are Maritime Air Masses from the North Atlantic of Only

Why are maritime air masses from the north Atlantic of only limited concern for weather in the U.S.?

A) Temperatures are usually mild over this region.
B) Question is incorrect;these air masses are very important.
C) Prevailing winds move them away from the U.S.
D) They never cause severe storms.
E) Polar fronts block these air masses from the U.S.